In the description herein, an aggregate of minute metal wires having a thickness of approximately 200 nm or less is referred to as “nanowires”. In comparison to powder, the respective wire correspond to “particle” constituting the powder, and the nanowires correspond to “powder” as an aggregate of particles.
Silver nanowires are expected as a conductive material for imparting conductivity to a transparent substrate. By coating a fluid containing silver nanowires (i.e., a silver nanowires ink) on a transparent substrate, such as glass, PET (polyethylene terephthalate) and PC (polycarbonate), followed by removing the liquid component by evaporation or the like, the silver nanowires are in contact with each other on the substrate to form a conductive network, thereby achieving a transparent conductor. For a transparent conductive material, a metal oxide film represented by ITO has been mainly used for such purposes as a transparent electrode. However, a metal oxide film has defects including the high film forming cost, the low resistance to bending, which may prevent the final product becoming flexible, and the like. A conductive film for a touch-sensitive panel sensor, which is one of the major applications of a transparent conductor, is demanded to have high transparency and high conductivity, and the demand in visibility thereof is also increasing in recent years. An ordinary ITO film necessarily has an increasing thickness of the ITO layer for enhancing the conductivity thereof, but the increase of the thickness may decrease the transparency, and the visibility may not be improved.
Silver nanowires are expected to avoid the aforementioned defects peculiar to a metal oxide film represented by ITO.
A known production method of silver nanowires include a method of dissolving a silver compound in a polyol solvent, such as ethylene glycol, and depositing metallic silver having a linear shape by utilizing the reduction power of the polyol as the solvent in the presence of a halogen compound and PVP (polyvinylpyrrolidone) as an organic protective agent (PTLs 1 and 2 and NPT 1). PVP is a substance that is considerably effective as an organic protective agent for synthesizing silver nanowires with good yield.